Vasomotor reactivity, which can be defined as the cerebral vasculature response to hypoxia, is not well known in epilepsy patients. We aimed to evaluate cerebrovascular reserve in idiopathic generalized epilepsy patients using transcranial Doppler ultrasonography (TCD). The study included 20 patients and 20 healthy volunteers. Diagnosis of epilepsy was based on the observation of seizure in the video electroencephalography unit. Cerebrovascular reactivity was evaluated by means of the breath-holding index. Insonation depth and basal velocity were symmetrical and not significantly different between the two groups (p[0.05). The breath-holding index ranged from 0.62 to 4.45 (mean 2.13 +/- 0.83) in the epilepsy patients and 0.57 to 2.55 (mean 1.60 +/- 0.46) in the control group (p\0.05). Breath-holding index values showed that cerebrovascular reserve in epilepsy patients was increased, as compared to healthy individuals. Cerebrovascular reserve was increased in epilepsy patients; this should not be accepted as an abnormality, but might have been the result of an adaptive mechanism that protects the brain from hypoxic challenges due to seizure apnea.